Process for the sensitization of photoconductors



United States Patent Hill NJ.

No Di'awing. Original application July 24, 1961, Ser. No. 125,984. Divided and this application Jan. 18, 1965, Set. No. 426,385

Claims priority, application Germany, May 29, 1959, 30 Claims. (:1. 96-1) This application is a division of copending application Serial No. 125,984, filed July 24, 1961, now abandoned, which, in turn, is a continuation-in-part of application Serial No. 30,752, filed May 23, 1960, and also now abandoned.

Electrophotographic material normally consists of a support on which there is a photoconductive substance, this coating being provided in the absence of light with an electrostatic charge. Then, the material is exposed to light behind a master, or an episcopic image is projected thereon, so that an electrostatic image is formed which corresponds to the master. This image is developed by being briefly contacted with a resin powder, whereupon a visible image is formed which is fixed by heating or by the action of solvents. In this way, an image of the master which is resistant to abrasion is obtained electrophotographically.

In the electrophotographic process as described an increase in the sensitivity of the photoconductive coatings has already been attempted by the addition of organic dyestufis, e.g. triphenylmethane, xanthene, phthalein, thiazine and acridine dyestulfs, to the photoconductors.

The absorption maxima of the organic photoconductors are mostly in the ultra-violet region of the spectrum. The addition of these dyestufi sensitizers achieves the result that the photoconductors become sensitive to visible light. Generally, the dyestulf sensitizers cause a displacement of the available sensitivity from the ultraviolet region to the visible region. With increased addition of dyestuff sensitizer, the sensitivity to visible light at first increases rapidly, but further additions give an increase in sensitivity which is much less than would be expected, and still further additions finally give no appreciable increase in sensitivity. The dyestuif sensitizers have the disadvantage that they color the coating considerably. In practice, the maximum achievable increase in sensitivity can seldom be utilized because then the photoconductor coatings have an intensity of color that is undesirable. Colorless or practically colorless photoconductor coatings are desired, since colored material can be employed only in special cases. If additions of dyestutf sensitizers are such as not to adversely atfect the coloring of the coating for practical purposes, the sensitizing effect often does not meet the demands of general usage. Further, the dyestutf sensitizers have the disadvantage that they bleach out relatively quickly so that their sensitizing action tends to be lost during the storage of the electrophotographic material.

A process for the sensitization of photoconductor coatings has now been found in which organic substances, containing polarizing residues and being capable of serving as electron-acceptors in a molecule complex, having low molecular weight, i.e. being non-resinous, being colorless or of pale color and having a melting point above room temperature, are added to the photoconductor coatings.

Substances which are primarily of interest as photoconductor coatings in accordance with the present process are those which can serve as electron donors in mole- Patented Nov. 22, 1966 cule complexes of the donor/acceptor type (known as 1r-complex) and contain at least one aromatic or heterocyclic ring, which may be substituted. Such photoconductors include aromatic hydrocarbons such as naphthalene, anthracene, benzanthrene, chrysene, p-diphenylbenzene, diphenyl anthracene, p-terphenyl, p-quaterphenyl, sexiphenyl; heterocycles such as N-alkyl carbazole, thiodiphenylamine, oxadiazoles, e.g., 2,5-bis-(p-aminophenyl)-l,3,4-oxadiazole and its N-alkyl and N-acyl derivatives; triazoles such as 2,5 bis-(p-aminophenyl)- 1,3 ,4-triazole and its N-alkyl and N-acyl derivatives; imidazolones and imidazolthiones, e.g., 1,3,4,5-tetraphenyl-imidazolone-2 and 1,3,4,5-tetraphenyl-imidazolthione-Z; N-aryl-pyrazolines, e.g. 1,3,5-triphenyl-pyrazoline; hydrated imidazoles, e.g., 1,3-diphenyl-tetrahydroimidazole; oxazole derivates such as 2,5-diphenyloxazole-2- p-dimethylamino-4,5-diphenyloxazole; thiazole derivatives such as 2-p-dialkylaminophenyl-methyl-benzthiazole; as also the following:

Oxazoles and imidazoles described in German patent application K 35,586 Iva/57b, filed Aug. 22, '1958. Acylhydrazones described in German patent application K 36,517 Iva/57b, filed Dec. 19, 1958.

2,2,4-triazines described in German patent application K 36,651 Iva/57b, filed Jan. 7, 1959.

Metal compounds of mercapto-benzthiazole, mercaptobenzoxazole and mercapto-benzimidazole described in German patent application K 37,508 Iva/57b, filed Apr. 18, 1959.

Imidazoles described in German patent application K 37,435 Iva/57b, filed Apr. 9, 1959.

Triphenylamines described in German patent application K 37,436 Iva/57b, filed Apr. 9, 1959.

Furans, thiophenes and pyrroles described in German patent application K 37,423 Iva/57b, filed Apr. 8, 1959.

Amino compounds with multinuclear heterocyclic and multinuclear aromatic ring system described in Gerpatent application K 37,437 lVa/ 57b, filed Apr. 9,

Azomethines described in German patent application K 29,270 Iva/57b, filed July 4, 1956.

Molecule complexes are defined in H. A. Staabs Einfuhrung in die theoretische organische Chemie (Introduction to Theoretical Organic Chemistry), Verlag Chemie, 1959, pp. 694-707, and by L. I. Andrews, Chemical Review, vol. 54, 1954, pp. 713-777. In particular, the donor/ acceptor complex (w-complexes") and "charge-transfer complexes which are formed from an electron-acceptor and an electron-donor are included. In the present case, the photoconductors are the electrondonors and the substances here called activatorsto distinguish them from the dyestutf sensitizers--are the electron-acceptors. The electron-donors have a low ionizaq tion energy and have a tendency to give up electrons. They are bases in the sense of the definition of acids and bases given by G. N. Lewis (H. A. Staab, as above, p. 600). The electron-donors primarilyconcerned in the present case are the photoconductors described above. These photoconductors consist of aromatic or heterocyclic systems containing a plurality of fused rings, or, alternatively, single rings having substituents which facilitate further electrophilic substitution of the aromatic ring, socalled electron-repellent substituents, as described by L. F. and M. Fieser, Lehrbuch der organischen Chemie (Textbook of Organic Chemistry), Verlag Chemie, 1954, p. 651, Table I. These are, in particular, saturated groups, e.g., alkyl groups such as methyl, ethyl, and propyl; alkoxy groups such as methoxy, ethoxy and propoxy; carbalkoxy groups such as carbmethoxy, carbethoxy and carbpropoxy; hydroxyl groups, amino groups 3 and dialkylamino groups such as dimethylamino, diethylamino and dipropylamino.

The activators in accordance with the invention, which are electron-acceptors, are compounds with a high electron-affinity and have a tendency to take up electrons. They are acids in the sense of Lewis definition. Such properties are possessed 'by substances having strongly polarizing residues or groupings such as cyano and nitro groups, halogens such as fluorine, chlorine, bromine and iodine; ketone groups, ester groups, acid anhydride groups, acid groups such as carboxyl groups or the quinone grouping. Strongly polarizing electron-attracting groups of this type are described by L. F. and M. Fieser in the Lelirbuch der organischen Chemie, Verlag Chemie, 1954, p. 651, Table I. Of these substances with a melting point above room temperature (25 C.) are preferable, i.e. solid substances, because these impart a particularly long shelf life to the photoconductive coatings as a result of their low vapor pressure. Substances which are rather deeply colored such as quinones can be used, but those that are colorless or only weak in color are preferable. Their absorption maximum should preferably be in the ultra-violet region of the spectrum, i.e. below 4,500 A. Further, the activator substances in accordance with the present process should be of lower molecular weight, i.e. between about 50 and 5000, preferably between about 100 and 1000, because with activators of lower molecular weight it is possible for reproducible results to be obtained insofar as sensitivity is concerned. Also, the sensitivity remains constant over rather long periods, since substances of lower molecular weight, unlike those of high molecular Weight, undergo hardly any change during storage. The following are examples of such substances:

1,5-dichlornaphthalene- 1,8-dichlorcuaphthalene. 2,4-dinitro-1-chloronaphthalene.

3,4-dichloro-nitrobenzene Tetrachlorophthalic anhydride.

Tetrabromophthalic anhydride.

Tetraiodophthalic anhydride.

Tetrachlorcphthalic acid monoethylester 2,4 dichlorobenzisatin Tetrabromophthalic acid monoethylester. 2,6-dichloro-benzaldehyde Tetraiodophthalic acid mono- I ethylester. Hexabromonaphthalic anhydride Iodotorm. bz-bcyano-benzanthronenfl Fumaric acid dinitrile.

Cyan acetic acid Tetracyanethylene.

2-cyanccinnamic acid.

s-Tricyano-benzene. 1,5-dlcyanonaphthalene- 3,5-dinitrobenzoic acid 2,4-dinitro-l-chloronaphthalene. 3,5-dinitrosalicylic acid 1,4-dinitro-naphtha1ene. 2 4-dinitro-1-benzoic acid 1,5-dinitronaphthalene.

1,8-dinitro-naphthalene.

2:4-dinitro-1-toluene-fi-sulfonic acid.

2-nitrobenzoic acid.

2,6-di1itro-1-phenol-4-sulphonic a 1,3-dinitro-benzene. 3-nltrobenzoic acid. 4,4'-dinitro-biphenyl 4-nitrobenzoic acid. 3-nitro4-methoxy-ben 8n.itro-4-ethoxy-benzoic acid. 4-nitro-l-1nethyl-benzoic acid 3-nitro2-cresol-5-sulphonic acid. G-mtro--methyl-l-phenol-Zsul- -nitrobarbituric acid. phonic acid. 2-nitrobenzenesulphinic acidinitro-acenaphthene. 3-nitro-2-hydroxyl-1-benzoic acid 4-nitro-benzaldehyde. z-nitro-l-phenol-ksulphonic acid.-. 4-nitro-phenol. 3-nitro-N-butyl-carbazole Picryl chloride. 4nitrobiphenyl 2,4,7-trinitro-fiuorenone.

Tetranitrofluorenone. s-Trinitro-benzene. 2,4,6'trinitr0-aniso1e Anthraqumone 1-chloro-2-methyl-anthraquinone. .hnthraquinone-zcarboxylic acid--- Duroquinone. AnthraquincneQ-aldehyde 2,6-dichloroquinone.

Anthraquinone-Z-sulphonic acid amlide. Anthaquinone-2J-disulphonic 1,5-diphenoxy-anthraquinone.

2,7-dinitro-anthraquinone.

1,5-dlchlorc-anthraquinone.

1,4-dimethy1-anthraquinone.

Anthraquinone-2,7-disulphonic acid bis-anilide. Anthraquinone-2-sulphonic acid dimethylamide. Acenaphthenequinone 2,5drchIoro-benzoquinqne. Anthraquinone-Z-sulphom'c acid 2,3-d1chloro-naphthoqumone-l,4.

methylamide.

1,5-dichloro-anthraquinone. l-rnethyl-4-chloro-anthraquinona. Picric acid. I Z-methylanthraquinone. Naphthoquinone-1,2. Naphthoquinone-l,4. Pentacenequinone. Tetracene-7,12-quinone. 1,4-toluquinone. 2,5,7,10-tetrachl0ropyrenequiuone.

Acenaphthenequinonedichloride. Benzoqninone-1,4 i-nitro-l-phenol-2-sulphonic acid l ,2-benzanthraquinone Brornanil l-chloro-4-nitro-anthraquinone Chloranil l-chior-anthraquinone Chrysenequinone- Thymoqm'none The quantity of the solid, non-resinous, substantially colorless electron-acceptors (activators) which is best incorporated in the photoconductive coating to be sensitized is easily established by simple experiments. Thephotoconductive coating containing at least one photo-1 conductor and at least one solid, non-resinous, substantially colorless, electron-acceptor, should contain the photoconductor and electron-acceptor in proportions ranging from substantially less than equal amounts to a substantial excess of the photoconductor with respect to the electron-acceptor. The optimum of the proportions varies somewhat according to the substance used. Generally, minor amounts are used, i.e. from about 0.1 to

about 300 moles, preferably from about 1 to about.50 moles of electron-acceptor per 1000 moles of photoconductor. Alternatively, it has also been found that in the photoconductive coatings containing at least one photoe conductor and at least one solid, non-resinous, substana tially colorless electron-acceptor, it is also very useful to have present the photoconductor and the electron-ac ceptor in proportions ranging from substantially less than equal amounts to a substantial excess of the electronacceptor with respect to the photoconductor. These proportions in which minor amounts of the photoconq ductor are added to the activator vary according to the a ture usually increases, and in such cases coatings made;

therefrom are inferior.

Mixtures of several photoconductors and activator substances may also be used. Moreover, in addition to these substances, sensitizing dyestuffs may be added.

By means of the present process, photoconductor coatings can be prepared which have a high degree of lightsensitivity, particularly in the ultra-violet region, and which are practically colorless. There is the further possibility of the photoconductor coatings being thereby strongly activated in the ultra-violet region and atterv wards being invested with a high degree of sensitivity to visible light by a very small addition .of dyestufi sensitizer without it being necessary for so much dyestuff to be added that the coat-ing takes on a deep color. Also, it is possible, by means of activators, for photoconductors such as naphthalene, whose initial sensitivity is very slight, to be given adequate sensitivity for the production of satisfactory images by electrophotographic processes.

Furthermore, by addition of minor amounts of photoconductors to activators, photoconductive mixtures are obtained which have photoconductivity much higher than could be expected from the amount of the photoconductor added to the activator. A further increase in the photoconductivity may be obtained by the addition of dyestuif sensitizcrs in the same amounts as in the photoconductor-activator mixtures in which the photoconductor is present in a major amount.

The coatings are treated in other respects in accordance with the known processes of electrophotography, i.e. the photoconductor substances are used in the form of thin, coherent homogeneous coatings on a supporting material. The materials used as supports are primarily metals, such as aluminum, zinc, and copper; cellulose products, such as paper and cellulose hydrate; plastics, such as polyvinyl alcohol, polyarnides, and polyurethanes. Other plastics, such as cellulose acetate and cellulose butyrate, especially in a partially saponified form, polyesters, polycarbonates, and polyole-fins, if they are covered with an electroconductive layer or if they are converted into materials which have the above-mentioned specific conductivity, e.g. by chemical treatment or by introduction of materials which render them electrically conductive, can also be used, as well as glass plates. In general, materials are suitable the specific resistance of which is less than ohm-cm., preferably less than 10 ohm-cm.

If paper is used as the supporting material, it is preferably pretreated against the penetration of coating solutions, e.g., it can be treated with a solution of methyl cellulose or polyvinyl alcohol in water or with a solution of an interpolymer of acrylic acid methyl ester and acryloni-trile in a mixture of acetone andmethylethyl ketone, or with solutions of polyamides in aqueous alcohols or with dispersions of such substances.

For the preparation of the electrophotognaphic material, the photoconductive compounds are preferably dissolved in organic solvents such as benzene, acetone, methylene chloride or ethyleneglycol monomethylether or other organic solvents or in mixtures of such solvents, and resins and the activatorsancl possibly also the dyestufi sensitizers-are advantageously added thereto. These solutions are coated upon the supporting material in the normal manner, e.g., by immersion processes, painting or roller application or by spraying. The material is then heated so that the solvent will be removed.

A number of the compounds in question can be applied together to the supporting material or the compounds can be applied in association with other photoconductive substances.

Further, it is often advantageous for the photoconductor substances to be applied to the supporting material in association with one or more binders, e.g., resins. Resins primarily of interest as additions to the photoconductor coatings include natural resins such as balsam resins, colophony and shellac, synthetic resins such as coumarone resins and indene resins, processed natural substances such as cellulose ethers; polymers such as vinyl polymers, e.g. polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyvinyl acetals, polyvinyl alcohol, polyvinyl ethers, polyacrylic and polymethacrylic acid esters, isobutylene and chlorinated rubber.

If the photoconductive compounds in accordance with the invention are used in association with the resins described above, the proportion of resin to photoconductor substance can vary very greatly. Mixtures of from two parts of resin and one part of photoconductor substance to two parts of photoconductor substance and one part of resin are .to be preferred. Mixtures of the two substances in equal parts by weight are particularly favora ble.

For the displacement of sensitivity from the ultra-violet to the visible range of the spectrum, dyestuif sensitizers can be used in addition to the activators. Even very small additions of sensitizer, e.g., less than 0.01 percent, give good results. In general, however, 0.01 to 5 percent, and preferably 0.1 to 3 percent of dyestulf sensitizer is added to the photoconductor coatings. The addition of larger quantities is possible but in general is not accompanied by any considerable increase in sensitivity.

Some examples are given below of dyestufi sensitizers which may be used with good results, and some with very good results. They are taken from Schultz Farbstolftabellen (7th edition, 1931, 1st vol.):

Triarylrnethane dyestulfs such as Brilliant Green (No. 760, p. 314), Victoria Blue B (No. 822, p. 347), Methyl Violet (No. 783, p. 327), Crystal Violet (No. 785, p. 329), Acid Violet 6B (No. 831, p. 351); xanthene dyestuffs, namely rhod-amines, such as Rhodamine B (No. 864, p. 365), Rhodamine 6G (No. 866, p. 366), Rhodamine G Extra (No. 865, p. 366), Su-lphorhodamine B (No. 863, p. 364) and Fast Acid Eosin G (No. 870, p. 368), as also phthaleins such as Eosin S (No. 883, p. 375), Eosin A (No. 881, p. 374), Erythrosin (No. 886, p. 376), Phloxin (No. 890, p. 378), Bengal Rose (No. 889, p. 378), and Fluorescein (No. 880, p. 373); thiazine dyestuffs such as Methylene Blue (No. 1038, p. 449); acridine dyestuffs such as Acridine Yellow (No. 901, p. 383), Acridine Orange (No. 908, p. 387) and Trypaflavine (No. 906, p. 386); quinoline dyestuffs such as Pin-acyanol (No. 924, p. 396) and Cryptocyanine (N0. 927, p. 397.); cyanine dyestufis, e.g., Cyanine (No. 921, p. 394) and chlorophyll.

For the production of copies with the electrocopying material, the photoconductive coating is charged by means of, for example, a corona discharge with a charging apparatus maintained at 6000-7000 volts. The electro-copying material is then exposed to light in contact with a master. Alternatively, an episcopic or diascopic image is projected thereon. An electrostatic image corresponding to the master is thus produced on the material. This invisible image is developed by contact with a developer consisting of carrier and toner. The carriers used may be, for example, tiny glass balls, iron powder or tiny plastic balls. The toner consists of a resin-carbon black mixture or a pigmented resin. The toner is used in a grain size of l to The developer may also consist of a resin or pigment suspended in a non-conductive liquid in which resins may be dissolved. The image that is made visible by development is then fixed, e.g., by heating with an infra-red radiator to 100170 C., preferably l20-150 C. or by treatment with solvents such as trichloroethylene, carbon tetrachloride or ethyl alcohol, or steam. Images corresponding to the master characterized by good contrast effect are obtained.

If trans arent supporting material is used, the electrophotographic images can also be used as masters for the production of further copies on any type of light-sensitive sheets.

If translucent supports are used for photoconductive layers such as are provided by the invention, reflex images can be produced also.

The application of the activators in accordance with the present process is not restricted to electrophotographic coatings, but can extend to other devices containing photoconductors, e.g., photoelectric cells, photoresistances, sensing heads or camera tubes and electroluminescent apparatus.

The invention will be further illustrated by reference to the following specific examples:

EXAMPLE 1 A solution containing 26 parts by weight of polyvinyl acetate (e.g., Mowilith 50), 25.6 parts by weight of naphthalene, 0.0415 part by weight of 2,3,7-trinitrofiuorenone and 800 parts by volume of toluene is applied by means of a coating device to an aluminum foil. After the coating has dried, direct images are produced thereon by the electrophotographic process in the following manner: the coated foil is given a negative electric charge by corona discharge, exposed behind a master to the light of a high-pressure mercury vapor lamp watts, at a distance of 30 cm.) for about 10 seconds and then dusted over with a developer.

The developer consists of tiny glass balls and a mixture of resin and carbon black which has been melted together and then finely divided. A developer of this sort consists of, e.g., 100 parts by Weight of tiny glass balls (grain size: 100-400p. approx.) and a toner (grain size: 20-50;!

approx). The toner is prepared by melting together 30 parts by weight of Polystyrol LG, 30 parts by weight of modified maleic acid resin (Beckacite K 105) and 3 parts by weight of Peerless Black Russ 552. The melt is then ground and screened. The finely divided resin adheres to the parts of the coating not struck by light during the exposure and a positive image of the master becomes visible. It is slightly heated and thereby fixed.

- If 2,4,7-trinitrofluorenone is not added to the coatings described above, even an exposure of two minutes will i not produce an electrophotographic image.

' EXAMPLE 2 veloper;

EXAMPLE 3 A solution of 26 parts by weight of polyvinyl acetate, 17.8 parts by weight of anthracene and 0.3357 part by weight of hexabromonaphthalic anhydride in 800 parts by volume of toluene is applied to aluminum and further procedure is as described in Example 1. With a 125-watt high-pressure mercury vapor lamp, the exposure time is 4 seconds.

8 EXAMPLE 1 s A solution of 26 parts by weight of polyvinyl acetate,

21.6 parts by Weight of 1,5-diethoxynaphthalene and 0.258 part by weight of 1,2-benzanthraquinone in 800 parts by volume of toluene is applied to paper and the matenal is further processed as described in Example 1.

The exposure time (125-watt high-pressure mercury vapor lamp) is 20 seconds.

Without the 1,2-benzanthraquinone addition, the copy still has considerable background after an exposure of 80 seconds.

EXAMPLE 6 '26 parts by weight of polyvinyl acetate, 17.8 parts by weight of phenanthrene and 0.245 part by Weight of chloranil are dissolved together in 800 parts by volume of toluene. The solution is applied to a superficially roughened aluminum foil and then the material is furtherprocessed as described in Example 1. If. the material is exposed to a 125-watt high-pressure mercury vapor lamp, an exposure of 10 seconds gives an image free of background and rich in contrast, Whereas Without the chloranil addition there is heavy background even after an exposure of one minute.

EXAMPLE 7 A solution containing 26 parts by Wei ht of l in I acetate, 24.4 parts by weight of o-dianisi t iine an i i fi b part by weight of dibromomaleic anhydride in 800 parts by volume of toluene is applied to an aluminum foil and the material is further processed as described in Example l. The exposure time (l25-watt high-pressure mercury vapor lamp) is 2 seconds. Without the dibromomalerc anhydride addition, it is 10 seconds.

TABLE A No. A B C D E 1 Polyvinylacetate 10 parts (1) 8 2 s Anthraquinone, 0.08 $823 18 (08'). s Anthraquinone, 0.17 20 see: (b) 8 Anthraquinone, 0 26 20 see. (b): 5 8 0. 001 60 see. (b). 6 s 0. 005 60 see. (b). 8 0.010 60 see. (b). g g see. (b). 8 Anthraquinone, 0.17 0: 001 20 :31 3 (ln 0. 010 20 see. (b). 8 20 see. (b). d 8 240 see. (a). 8 180 see. (a). Cycgzed rubber, 10 parts g 240 O a Aiterchlorinated polyvinylehloride, 7 parts (a s Polyvinylehloride, afterehlorinated, 7 Parts 3 3 See Maleic acid resin, 10 parts (4) 8 240 sc 8 Anthraquiuone, 0.25 part 60 sec (3) 21 Chlorinated rubber, in parts (5) 8 20 see 22 00,10 8 Anthraquinonc, 0.25 part 10 sec (3) 23 Chlorinated rubber, 10 parts (6) 8 20 Sec. 2L 8 Anthraquinone, 0 5 10 sec: (8) 8 1.2-benzanthraqulnone, 0.31 part 11.5 see. (a) 8 Hexabromonaphthalic anhydride, 0.80 part 11.5 sec. (11) 8 2,$5,7-tetran1trofluorenone, 0.43 part 1.5 see, (a) 8 D bromomalelc anhydride, 0.30 part 4-6 sec. (3) 8 Nitroiterephthallc acid-dimethylester, 0.28 6-8 see. (a).

par Y 8 Tetracyano ethylene 0.15 part 4- 3L s 1,3,5-trlnltrobenzene, 0.25 part. 1.5 c l;

Without the hexabromonaphthalic anhydride addition, an exposure of as much as 30 seconds gives an image which contains background.

EXAMPLE 4 Explanations on Table A Column A: Quantity and kind of binder used. -In all cases, the quantities stated were dissolved in 200 parts by volume of toluene.

Column B: Quantity of the photoconductor. In all examples, the same amount of pyrene was used. Column C: Quantity of the activator used.

Column D: Quantity of dyestuff sensitizer used (Rhodamine B extra).

Column E: Time of exposure, using:

(a) a 250 watt photographic lamp (Philips Photocrescenta) (b) a customary watt incandescent lamp.v

The tests were carried through under the same experimental conditions, with the exception of the variations stated in the table.

1) The polyvinyl acetate used was the product commercially available under the registered trademark Mowilith C.

(2) The cyclized rubber used was the product commercially available under the registered trademark Pliolite S-SD.

(3) The afterchlorinated polyvinylchloride used was the product commercially available under the registered trademark Rhenoflex.

(4) The maleic acid resin used was the product commercially available under the designation Alrosat.

(5) The chlorinated rubber used in Table A, col. A, under N0. 21 (5) was the product commercially available under the registered trademark Parlon S5 cps.

(6) The chlorinated rubber used in Table A, col. A, under N0. 23 (6) was a product commercially available under the registered trademark Pergut 8-40.

The following Table B shows further examples of various photoconductors which were activated, and the reduction in exposure time caused by the activators:

TABLE B A B G 26 Chloranil Hexabromonaphthalic anhydride 2,4,5,7-tetranitrofluorenone Hexabromouaphthalic anhydride.

2,4,5,7-tetranitrofluorenone 13.6 hydroquinonedimethylether.

25.6 naphthalene- 26 21.61,5'diethoxynaphtha- 26 lene.

15.4 acenaphthene' 26 15.2 aoenaphtbylenefinn 15.4 diphenyl 18 24.4 o-dianisidine 16.6 fiuorene 26 17.8 anthracene 26 2,4,5,7-tetranitrofluorenone Benzoquinone Chloranil 3,5-dinitrosalicylic acid 1,2-benzanthraquinone- Tetrachlorophthalic anhydride Hexabromonaphthalic anhydride Picrylchloride 2,4,5,7-tetranitrofluorenone-- Benzoquinone Chloranjl 2,4,5,7-tetranitrofiuorenone 1,4-benzoquinone Chloranil 3,5-dinitrosalicylic acid 1.2-benzanthraquinone. Dibrornomaleic acid anhydnde. Tetrachlorophthalic anhydride.--. Hexabromonaphthalic anhydrlde Picrylchloride 2,4,5.7-tetranitrofiuorenone 1,2-benzanthraquinone Dibromomaleic anhydride Tetrachlorophthalic anhydride- Hexabromonaphthalic anhydride Picrylchloride 2,4,5,7-tetranitrofluorenone 22.8 chrysene 52 16.9 diphenylamine 26 26.9 2,2-dinaphthylami.ne-

17.8 phenanthrene 26 TABLE BContinued A B C Chloram'l 1,2-beuzanthraquinone. Dibromomaleic auhydride. Tetrachlorophthalic anhydride Hexabromouaphthalic anhydride Picrylchlori e 19.3 2-phenyl-iudole 26 19.9 thiodipheuylamine- 25.48 2,4-bis-(4-diethylaminophenyl) -1,3,4 oxadiazole.

18.2 2,4-bts-(4'-diethylaminopheny1)-1,3,4- triazole.

Explanations on Table The table describes a series of experiments carried through for improving the photoconductivity of organic substances by adding activators.

In Column A the quantity and nature of the substance used is stated. The substances marked with a yielded no electrophotographic images even after an exposure time of several minutes.

In Column B the quantity of the binder used is stated. In all of the cases, polyvinyl acetate having a K-value of 50 was used. Binder, photoconductive substance, and activator were dissolved in toluene, coated onto an aluminum foil, and dried.

In Column C the substance used as activator is stated. In all of the cases 1 mol of the activator stated under C was used per moles of the substance stated under A.

In Column D the reduced time of exposure is stated which is required to produce images equal in quality to those produced without the addition of an activator. In those cases where a prolonged exposure of the photoconductor yielded not even a weak image (marked with a the calculation of the reduced time of exposure was based on the longest exposure used for the unactivated photoconductor substance.

Alternatively, the increase in sensibility obtained by the addition of activating substances may be taken from a comparison of the degrees of blackening obtained with the activated photoconductive layer and with the unactivated photoconductive layer, under the same customary step wedge (e.g. Kodak No. 2 density strip with color patches).

EXAMPLE 8 A solution containing 20 parts by weight of afterchlorinated polyvinyl chloride with a content of chlorine from 61.7 to 62.3 percent and K-value from 59 to 62, 18.01 parts by weight of 2,4,5,7-tetranitrofiuorenone and 0.216 part by weight of 1,5-diethoxynaphthalene dissolved in a mixture of 450 parts by volume toluene and parts by volume butanone is applied to an aluminum foil. The subsequent procedure is that described in Example 1. The exposure time, with a 100 watt incandescent lamp at a distance of 30 centimeters is 2 seconds.

Without the addition of 1,5-diethoxynaphthalene the exposure time is about 40 seconds.

11 In the following table, the exposure times are given, which were obtained When using other photoconductors instead of the 1,5-diethoxynaphthalene.

Exposure time EXAMPLE 9 A solution of 12 parts by weight of chlorinated rubber (Pergut S40), 5.04 parts by weight of 1,3dinitrobenzene and 0.106 part by weight of anthracene in 150 parts 1'2 2,2-dinaphthylamine, the exposure time is about 10 seconds.

EXAMPLE 12 To a solution containing 28.6 parts by weight of tetrachlorophthalic acid anhydride and 20 parts by weight of afterchlorinated polyvinyl chloride in a mixture of 150 parts by volume of butanone and 450 parts by volume of toluene, X parts by weight of photoconductor and.

Y parts by weight of dyestufi sensitizer are added. In the following table, the amounts of the photoconductor and sensitizer are given together with the corresponding exposure times. It is advantageous to dissolve the dyestuif sensitizer in a small amount of ethyleneglycol monomethyl ether before adding it to the solution. The latter is applied to a paper base material and further processed as described in Example 1. The light source used throughout was a 125-watt high pressure mercury vapor lamp and the distance between this lamp and the material exposed was about 30 centimeters.

by l f of toluene is applied to P P foil and the PhotoconductorXparts Dyestufi SensitizerY Exposure materlal 1s further processed as described 111 Example 1. by weight Parts by weight sTime The exposure time (125 watt high pressure mercury vao s) por lamp) is 20 seconds. Without the anthracene addr- N N 2 0 ion. v n f r n p r tune of 80 seconds, a eit t'ryiearrzar jj'"'1 3385;133:533;"21:": "9 o 0.30 Rh dam e e ra 2-3 traces of an image were obtained. Thls me n t t e 0.54 mhdinaphthylam. None"? H exposed parts of the coating were not drscharged and 30,: 2 therefore still attracted developer. -g gatgge t g ag mo- None 4 In the following table the exposure times are given, B 030 RhodammeBext-mun o 0.025 Basischreinblau 3 G.-- 2 which were obtamed, when using other photoconductors DO" M15 Brinamgreen extra 3 instead of the 1,3-d1mtrobenzene. go" 0.015 Kristallviglet 2 Exposure time 0 0-0 5 Methy Il 119 0.5 0.39 01 -N-vm lea b le. 0.30 Rh d eBe t 9 Photoconductors (parts by weight): (seconds) 50?: N nejfff 20 2,2-dinaphthylamine (0.180) 20 2,5-bis-(4'-diethylaminophenyl)-1,3,4 oxdiazole EXAMPLE 10 EXAMPLE 13 A solution containing 20 parts by weight of the afterchlorinated polyvinyl chloride mentioned in Example 8, 21.02 parts by weight of benzile and 0.370 part by weight of benzidine in a mixture of 450 parts by volume of toluene and 150 parts by volume of butanone is applied to an aluminum foil and the material is further processed as described in Example 1. The exposure time (125 watt high pressure mercury vapor lamp at a distance of 30 centimeters) is 10 seconds. Without the addition of the benzidine activator, even after an exposure time of 4 minutes, no electrophotographic image could be obtained.

In the following table, the exposure times are given which were obtained when using photoconductors other than benzidine.

Exposure time Photoconductors (parts by weight): (seconds) 2,2'-dinaphthylamine (0.540) 20 2,5-bis-(4'-diethylamino-phenyl) 1,3,4 oxdiazole (0.730) 5 Poly-N-vinylcarbazole (0.390) 30 EXAMPLE 11 the oxdiazole compound, even after an exposure time of 40 seconds, no image could be obtained. When the oxdiazole compound is replaced by 0.120 part by weight of A solution is prepared, containing 57.2 parts by weight of tetrachlorophthalic acid anhydride and 65 parts by weight of afterchlorinated polyvinyl chloride in 700 parts by volume toluene and suflicient butanone is added ,to make up 1000 parts by volume. To 50 parts by volume of the resulting stock solution, one of the photoconductors listed below is added, and the solution is applied to an aluminum foil and further processed as described in Example 1. In the following table, the added photoconductors are indicated, and the corresponding exposure times are given. As the light source, a l25-watt high pressure mercury vapor lamp in a distance of about 30 centimeters from the exposed material Was used in all instances.

Exposure time 1 Image with heavy background,

13 Photoconductor (parts by weight) Exposure time Continued (seconds) Phenanthrene (0.089) 60 Phenoxathin (0.100) 10 Stilbene (0.090) 30 2,3,5-triphenylpyrrole (0.153) l 1,1-dinaphthylamine (0.134) 30 1,2'-dinaphthylamine (0.134) 30 4'-tolyl-l-naphthylamine (0.116) 60 Z-phenylindole (0.096) 60 Acenaphthene (0.077) 60 Diphenyl (0.077) 120 N-methyldiphenylamine (0.091) 30 4-hydroxy-diphenylamine (0.092) 3O Phlorglucinediethylether (0.091) 120 EXAMPLE 14 57.2 parts by weight of tetrachlorophthalic acid anhydride and 65 parts by weight of polyvinyl acetate are dissolved in suificient toluene to make up 1000 parts by volume. To 50 parts by volume of this stock solution, one of the photocondnctors listed below is added and the coating solution is applied to an aluminum foil and further processed as described in Example 1. The light source and the distance of the light source from the exposed material were the same as in the foregoing example.

Exposure time (seconds) Photoconductor (parts by weight) None Naphthalene (0.064) Hydroquinonedimethyl ether (0.069) N-ethylcarbazole (0.097) Anthracene (0.089) Carbazole (0.081) Chrysene (0.114) Pyrene (0.101) o-Dianisidine (0.122) 1,5-diethoxynaphthalene (0.101) 2,6-dimethyl-naphthalene (0.078) Hexamethylbenzene (0.081) 2,2'-dinaphthylamine (0.134) Diphenylamine (0.084) Diphenyleneoxide (0.084) Indole (0.058) Fluorene (0.083) Stilbene (0.090)

EXAMPLE 15 29.62 parts by weight of phthalic acid anhydride and 33 parts by weight of afterchlorinated polyvinyl chloride are dissolved in 670 parts by volume of toluene and 330 parts by volume of butanone. To 50 parts by volume of the resulting stock solution, one of the photoconductors listed in the following table is added; these coating solutions are applied to an aluminum foil, and further processed as described in Example 1. The light source and the distance of the light source were the same as in Example 13.

Exposure time Photoconductor (parts by weight): (seconds) None 1 60 N-ethylcarbazole (0.10) 5 Anthraoene (0.09) Chrysene (0.114) Pyrene (0.10) 10 2,2-dinaphthylamine (0.134) 10 2,3,5-tn'phenylpyrrole (0.153) 10 1 No image obtained.

EXAMPLE 16 49.2 parts by weight of chloranil and 56 parts by weight of afterchlorinated polyvinyl chloride are dissolved in a mixture of 1170 parts by volume of toluene and parts by volume of butanone. The resulting solution is filled up to 2000 parts by volume with chlorobenzene. To 100 parts by volume of this stock solution, one of the photoconductors listed in the following table is added; the coating solution is applied to an aluminum foil and further processed as described in Example 1. The light source and the distance of the light source were the same as in Example 13.

10.6 parts by Weight of 2-acetyl fluorene and 12 parts by weight of afterchlorinated polyvinyl chloride are dissolved in parts of toluene and sutficient butanol to make up 250 parts by volume of solution. To 50 parts by volume of this stock solution, one of the photoconductors of the following table is added. The solution is applied to an aluminum foil and further processed as described in Example 1. The light source and the distance of the light source were the same as in Example 13.

. Exposure time Photoconductor (parts by weight): (seconds) None 1 180 o-Dianisidine (0.120) 30 2,5 -bis- 4'-diethylaminophenyl) -1,3,4-oxdiazole 1 No image obtained.

EXAMPLE 18 44 parts by weight of 9 acetyl-anthracene and 48 parts by weight of afterchlorinated polyvinyl chloride are dissolved in 700 parts by volume of solution. To 50 parts by volume of the resulting stock solution, one of the photoconductors of the following table is added. This solution is applied to an aluminum foil and further processed as described in Example 1. The light source and the distance thereof was the same as in Example 13.

Exposure time Photoconduotor (parts by weight): (seconds) None 1 180 Hydroquinonedimethyl ether (0.069) 30 N-ethyl carbazole (0.097) 60 Anthracene (0.089) 60 Hexamethylbenzene (0.081) 30 1 Image with heavy background.

EXAMPLE 19 46.2 parts by weight of pyrene3-aldehyde and 50 parts by weight of afterchlorinated polyvinyl chloride are dissolved in 670 parts by volume of toluene and suflicient butanol to make up 1000 parts by volume of solution. To 50 parts by volume of the resulting stock solution one of the photoconductors of the following table is added. The solution is applied to an aluminum foil and further processed as described in Example 1. The light source 15 and the distance of the light source were the same as in Example 13.

Exposure time Photoconductor (parts by weight): (seconds) None 30 Naphthalene (0.064) 20 Hydroquinonedimethyl ether (0.070) 20 N-ethylcarbazole (0.10) 10 Anthracene (0.090) 20 Chrysene (0.114) 20 Pyrene (0.10) 20 Hexamethylbenzene (0.080) 20 2,2-dinaphthylamine (0.135) 15 2,5-bis-(4'-diethylaminophenyl)-1,3,4-oxdiazole (0.180) 2,3,5-triphenylpyrrole (0.150) 20 EMMPLE 20 13.1 parts by weight of 1,4,5-trinitronaphthalene and 15 parts by weight of afterchlorinated polyvinyl chloride were dissolved in 180 parts by volume of toluene and sufficient butanone to make up 250 parts by volume. To 50 parts of the resulting stock solution, one of the photoconductors of the following table is added in the amount indicated. This solution ,is applied to an aluminum foil and further processed as described in Example 1. The light source and the distance thereof were the same as in Example 13.

Exposure time Photoconductor (parts by weight): (seconds) None 1 180 N-ethylcarbazole (0.10) 30 Anthracene (0.09) 30 o-Dianisldine (0.12)

' 2,5-bis-(4'-diethylaminophenyl) -1,3,4-oxdiazole 1 Image with heavy background.

It will be obvious to those skilled in the art that many modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.

What is claimed is:

1. A sensitized photoconductive layer comprising at least one solid, non-resinous, substantially colorless electron-acceptor and a compound having the formula in which R and R are selected from the group consisting of aryl and hetero cyclic groups, R is selected from the group consisting of hydrogen and alkyl groups, and R is selected from the group consisting of hydrogen, aryl and heterocyclic groups.

2. A sensitized photoconductive layer comprising at least one solid, non-resinous, substantially colorless electron-acceptor and a compound having the formula in which R and R are selected from the group consisting of aryl and heterocyclic groups, R is selected from the group consisting of hydrogen and alkyl groups, and R is selected from the. group consisting of hydrogen, aryl and heterocyclic groups; the layer containing the photoconductor and the electron-acceptor in proportions ranging from substantially less than equal amounts to a substantial excess of the photoconductor with respect to the electron-acceptor and from substantially less than equal amounts to a substantial excess of the electron-acceptor with respect to the photoconductor.

3. A sensitized photoconductive layer comprising at least one solid, non-resinous, substantially colorless elec tron-acceptor and a compound having the formula in which R and R are selected from the group consisting of aryl and heterocyclic groups, R is selected from the.

group consisting of hydrogen and alkyl groups, and R is selected from the group consisting of hydrogemaryl and heterocyclic groups; in proportions ranging from about 0.1 to about 300 moles of the electron-acceptor per 1000 moles of photoconductor. e

4. A sensitized photoconductive layer comprising at least one solid, non-resinous, susbtantially colorless electron-acceptor and a compound having the formula in which R and R are selected from the group consist ing of aryl and heterocyclic groups, R is selected from the group consisting of hydrogen and alkyl groups, and.

R is selected from the group consisting of hydrogen, aryl and heterocyclic groups; in proportions ranging from about 0.1 to about 300 moles of the photoconductor per 1000 moles of the electron-acceptor.

5. A sensitizedphotoconductive layer comprising at least one solid, non-resinous, substantially colorless electron-acceptor and a compound having the formula in which R and R are selected from the group consisting of aryl and heterocyclic groups, R, is selected from the group consisting of hydrogen and alkyl groups, and R is selected from the group consisting of hydrogen, aryl and heterocyclic groups; in proportions ranging from about 1 to about 50 moles of the photoconductor per i 1000 moles of the electron-acceptor.

7. A layer according to claim 1 in which the electronacceptor is 2,4,7-trinitrofluorenone.

8. A layer according to claim 1 in which the electronacceptor is tetranitrofiuorenone.

9. A layer according to claim 1 in which the electronacceptor is hexabromonaphthalic anhydride.

10. A layer according to claim 1 inwhich the electron-acceptor is tetrachlorophthalic anhydride.

11. A layer accord-ing to claim 1 in which the electronacceptor is 1,2-benzanthraquinone.

12. A layer according to claim 1 in which the electronacceptor is chloranil.

13. A layer according to claim 1 in which the electron-acceptor is di'bromomaleic anhydride.

14. A layer according to claim 1 including a resin.

15. A layer according to claim 1 including a dyestuff sensitizer.

16. A photographic reproduction process which comprises exposing an electrostatically charged, supported, photoconductive insulating layer to light under a master and developing the resulting image with an eleetroscopic material, the photoconductive layer comprising at least one solid, non-resinous, substantially colorless electronacceptor and a compound having the formula in which R and R are selected from the group consisting of aryl and heterocyclic groups, R, is selected from the group consisting of hydrogen and alkyl groups, and R is selected from the group consisting of hydrogen, aryl and heterocyclic groups.

17. A photographic reproduction process which comprises exposing an electrostatically charged, supported, photoconductive insulating layer to light under a master and developing the resulting image with an electroscopie material, the photoconductive layer comprising at least one solid, non-resinous, substantially colorless electronacceptor and a compound having the formula F-g-ih R C C-Rz in which R and R are selected from the group consisting of aryl and heterocyclic groups, R is selected from the group consisting of hydrogen and alkyl groups, and R is selected from the group consisting of hydrogen, aryl and heterocyclic groups; the layer containing the photoconductor and the electron-acceptor in proportions ranging from substantially less than equal amounts to a substantial excess of the photoconductor with respect to the electron-acceptor and from substantially less than equal amounts to a substantial excess of the electronacceptor with respect to the photoconductor.

18. A photographic reproduction process which comprises exposing an electrostatically charged, supported, photoconductive insulating layer to light under a master and developing the resulting image with an electroscopic material, the photoconductive layer comprising at least one solid, non-resinous, substantially colorless electronacceptor and a compound having the formula in which R and R are selected from the group consisting of aryl and heterocyclic groups, R is selected from the group consisting of hydrogen and alkyl groups, and R is selected from the group consisting of hydrogen, aryl and heterocyclic groups; in proportions ranging from about 0.1 to about 300 moles of the electron-acceptor per 1000 moles of photoconductor.

19. A photographic reproduction process which comprises exposing an electrostat-ically charged, supported, photoconductive insulating layer to light under a master and developing the resulting image with an electroscopic material, the photoconductive layer comprising at least one sol-id, non-resinous, substantially colorless electronacceptor and a compound having the formula in which R and R are selected from the group consisting of aryl and heterocyclic groups, R; is selected from the group consisting of hydrogen and alkyl groups, and R is selected from the group consisting of hydrogen, aryl and heterocyclic groups; in proportions ranging from about 0.1 to about 300 moles of the photoconductor per 1000 moles of the electron-acceptor.

20. A photographic reproduction process which comprises exposing an electrostatically charged, supported, photoconductive insulating layer to light under a master and developing the resulting image with an electroscopic material, the photoconductive layer comprising at least one solid, non-resinous, substantially colorless electronacceptor and a compound having the formula in which R and R are selected from the group consisting of aryl and heterocyclic groups, R is selected from the group consisting of hydrogen and alkyl groups, and R is selected from the group consisting of hydrogen, aryl and heterocyclic groups; in proportions ranging from about 1 to about 50 moles of the electron-acceptor per 1000 moles of the photoconductor.

21. A photographic reproduction process which comprises exposing an electrostatically charged, supported, photoconductive insulating layer to light under a master and developing the resulting image with an electroscopic material, the photoconductive layer comprising at least one solid, non-resinous, substantially colorless electronacceptor and a compound having the formula in which R and R are selected from the group consisting of aryl and heterocyclic groups, R is selected from the group consisting of hydrogen and alkyl groups, and R is selected from the group consisting of hydrogen, aryl and heterocyclic groups; in proportions ranging from about 1 to about 50 moles of the photoconductor per 1000 moles of the electron-acceptor.

22. A process according to claim 16 in which the electron-acceptor is 2,4,7-trinitrofluorenone.

23. A process according to claim 16 in which the elec' tron-acceptor is tetranitrofluorenone.

24. A process according to claim 16 in which the electron-acceptor is hexabromonaphthalic anhydride.

25. A process according to claim 16 in which the electron-acceptor is tetrachlorophthalic anhydride.

26. A process according to claim 16 in which the electron-acceptor is 1,2-benzanthraquinone.

27. A process according to claim 16 in which the electron-acceptor is chloranil.

28. A process according to claim 16 in which the electron-acceptor is dibromomaleic anhydride.

29. A process according to claim 16 in which the layer OTHER REFERENCES includes a resin. i i 30. A process according to claim 16 in which the layer fi Chemlcal Reviews 713 October mmdes a dyesmff Sensmzer' Czekalla et 211.: Chemical Abstracts, 52: 431711 1957?.

Ref Cited by the Examiner 5 Schneider and Compton et al.: Journal of Chemical UNITED STATES PATENTS Physlcs, V01. :25: 358, 1075-1076 (1956). 3,037,861 6/1962 Hoegl et a1. 961 1 3,113,022 12/1963 Cassiers et a1. 961 NORMAN TORCHIN Emmne" 3,155,503 11/ 1964 Cassiers et a1. 961 10 C. E. VAN HORN, Assistant Examiner. 

1. A SENSITIZED PHOTOCONDUCTIVE LAYER COMPRISING AT LEAST ONE SOLID, NON-RESINOUS, SUBSTANTIALLY COLORLESS ELECTRON-ACCEPTOR AND A COMPOUND HAVING THE FORMULA 